Comment by Blackthorn

It creates nested data without looking like the end format of the data (why I really can't get into jsonnet), it's just obviously its own language but is pretty minimal.

Despite the minimalism it is not necessarily simple. There are features like inheritance and late binding. They can be quite complicated, but the thing that really stands out about GCL is it's not complicated to use. The simple cases are easy, straightforward, and readable. The complicated cases are made possible.

I've used it extensively to store and transform data that has to be manually edited by humans. It's a really great format because I can define all the translation rules which can get pretty complicated, but the complexity I expose to the humans who are writing the data is minimal. But if they need to do some transformations on the data or even just, like, string substitutions...the language is there and they can use it. That's what makes writing your data in a configuration language nice.

(Honestly though I think jsonnet is at least vastly superior to skycfg and the whole starlark ecosystem. I swear I'm so sick of languages that intentionally look like Python without being actual Python!)